If you are not setting a string to a firebase tag using the firebase component, but calling the value back with the firebase component, then this will happen. You will need to add double quotes to your string before you send it.
Alternatively use the web component to return the value from a tag (although this does not provide for dataChanged events)
Hello, help me how to switch from one screen to another correctly so that at the end of the work, close the entire application with one click.
Search the community for switch screens
I found this @Anke extension very useful to close the application and leave no instance open when there are switchs between different screens »
And I found this 'Tribblehunter method' to make the switch between the screens, very functional *»
( * ) » Extracted from here » [App Inventor Tutorials and Examples: Multiple Screens | Pura Vida Apps]
To get out of the application, once its final process is completed, it is not necessary to use the [Close Application] Block (from the control drawer)... Just invoke the extension and call by [Close Screen] 
Lito
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Thanks, I've sorted out the screens. Now I have another problem. There is a text.csv on the flash drive. It is necessary to enter data from it into FIREBASE, I designate the data as //text.csv, but the program does not see them.
Do you refer to a USB Flash Drive?
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yes
You will need to use this @Taifun extension »
But this has nothing more to do with 'barcode scanning'...
Lito
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Error 908. Android 14.
I want to read the tovar.csv file in the DOWNLOAD directory
If your file tovar.csv, is not owned/created by your app, then you will need to use the SAF extension to read your file.
Select list item: Attempt to get item number 2 of a list of length 1: ["No content provider: /Download/tovar.csv"]
You have to access the file either with the filePicker or with the SAF Open Document block, then return the contenturi to the SAF ReadFromFile block. You cannot use normal filepaths.
Consider uploading your spreadsheet to Google Sheets, and downloading it from there using the Spreadsheet component.
That would avoid all file permission hassles.
Taifun
